Call him the sure thing. Adam Peaty won Great Britain’s first gold medal of these Games with an astonishing performance at the Aquatics Stadium. He did it in a world record time of 57.13sec, a full four tenths of second better than his record mark in the heats earlier in the week. In second place was a long stretch of water, and after that South Africa’s Cameron van der Burgh and then the USA’s Cody Miller.

Peaty’s was the first victory for a male British swimmer since Adrian Moorhouse won this same event back in 1988. And incredible as it seems to everyone who watched Britain’s men’s team swim in the six Games there have been since, it never felt in doubt. Before the race Peaty was 100-1 on with the bookmakers. And once he had taken the lead after 25m, his victory was a little less certain than death, and a touch more than taxes.

Adam Peaty breaks world record again on memorable evening for Britain

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You must have read or heard it said that the young don’t feel fear because they haven’t learned what it’s like to lose. Like a lot of the platitudes in this business, you don’t have to think too long or too hard to spot that it’s a lot of rot, that often as not they’ve even more to worry about than everyone else. Which is why we also wax on about the inexperience of youth, and the nerves you feel when you’re making your debut.

In Peaty’s case, though, that old line rings true. He doesn’t just say “pressure doesn’t exist”, he swims that way. Which is why he’s won every major 100m race he’s competed in since the summer of 2014. He’s one of those cold-blooded sorts, rare in British sport, who hardly seem to feel the heat. As he says, “I enjoy racing because I want to do it. No one’s forcing me. What’s the worst that could happen? You’re going to come second?”

Peaty’s coach, Mel Marshall always suspected he had the talent. Or almost always. She took two looks before she was sure. She first saw him swim when he was 14, just after he’d joined the City of Derby club. Peaty was swimming freestyle, badly, plowing his way up and down the slow lane. Marshall didn’t reckon much of him until he switched to breaststroke, and then she knew, straight away. She could see it in the strength of his lunge and the steady line he held through the water.

Marshall, who won 15 medals in her own international career, persuaded Peaty to commit to the breaststroke. But talent wasn’t enough on its own. It never is. And in 2012, Peaty wasn’t even close to the best breaststrokers in Britain. He finished 10h in the 100m at the national championships in April 2012, and wasn’t anywhere near making the Olympic team.

Peaty has said himself that he lacked the dedication he needed to succeed. In swimming, success costs a lot. All those hours in the pool, the starts at sunrise each morning and the twilight finishes every night, they leave little time for schoolwork or socialising. And while Peaty may have been happy enough to slack off one of the two, the other felt a harder sacrifice to make.

Adam Peaty celebrates with his gold medal. Photograph: Tom Jenkins for the Guardian

Later in 2012, during the Olympics, Peaty was just getting ready to go out – to “get drunk in a field or something stupid like that” – when he flicked on his phone to check what was happening in the swimming. He saw that his mate Craig Benson had made the semi-finals in Peaty’s favourite event, the 100m breaststroke. And that was the moment everything changed.

They knew each other well from the junior circuit. Benson is only eight months older than Peaty, but back then he was so much better. “It was like a ‘what am I doing with my life?’ kind of moment,” Peaty said later. “From then, I watched all the Olympics and said to myself that I would make the next one. That was my defining moment, to stop messing about and get my head down.”

He dropped out of college and started training full time. He married his incredible natural talent and impressively cool temper to an intense commitment to training. Back at the British National Championships the next year, Peaty finished third in the 100m breaststroke. A month later, he broke the minute barrier for the very first time at the National Youth Championships. In the circles of British swimming, people were starting to talk about his prospects.

Everyone else caught on one night at the Tollcross pool in Glasgow, during the Commonwealth Games in 2014. That was when Peaty had to race for the first time against his idol Van der Burgh, the Olympic champion. Peaty was only 19, but he beat Van der Burgh, and broke the Games’ record. After that he didn’t look back. At the European Championships the next month he won four gold medals, then in 2015 he broke Van der Burgh’s world record at the British Championship. Later that year he won three gold medals at the World Championships in Kazan, and then four more at the European Championships this spring.

Now he has the one that matters most of all. In the space of four years Peaty has gone from being just another British swimmer to the Olympic champion. Right now, the 21-year-old Peaty is one of the most impressive competitors in the country, in any sport.